This application claims the priority of German application 197 30 481.8, filed in Germany on Jul. 16, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for manufacturing a part in the shape of a hollow profile made of light metal or other materials of low elongation at rupture being expanded by internal high pressure shaping.
A method of this general type is known from DE 195 06 160 A1. In this method, parts in the shape of a hollow profile for a vehicle body made of aluminum, especially gusset elements in the frame structure, are manufactured by internal high-pressure shaping. However, manufacture of other light metal parts in which much higher degrees of shaping occur than the degree of shaping required to produce the final contours of gusset elements is not possible with conventional internal high-pressure shaping methods since because of the much lower elongation at rupture of light metals by comparison to that of steel materials for example, the bursting limit of hollow profiles is reached very quickly so that the material fails before the hollow profile comes in contact with the tool contour for producing the desired final shape. As a result, there is a high probability that rejects will be produced.
A goal of the invention is to improve on a method of the above noted type in such fashion that parts in the form of hollow profiles based on light metal or based on other materials with low elongation at rupture can be manufactured safely in simple fashion, even with high degrees of deformation.
This goal is achieved according to preferred embodiments of the invention by a method for manufacturing a part in the shape of a hollow profile, with a hollow profile made of light metal or other material of the hollow profile, or of other materials with low elongation at rupture being expanded by internal-high-pressure shaping, wherein a sleeve made of a material with a higher ductility than light metal, especially a steel material, is slid onto the hollow profile and is located on the hollow profile such that a predetermined area of the hollow profile is covered by the sleeve, with said predetermined area to be shaped during later expansion with a high degree of deformation that exceeds the expandability of the light metal, and wherein the hollow profile is expanded within this predetermined area by means of high internal pressure to a point beyond the burst limit, whereupon the sleeve is expanded alone, directly exposed to the high internal pressure above the burst point in the final-shaped hollow profile, until the final shape of the part is reached in the predetermined area that is held by the sleeve at both ends in a press fit on hollow profile.
By simply sliding a sleeve, available as a mass-produced product and made of a material that is more ductile than light metal, onto the light metal hollow shape, the area of the hollow profile covered by the sleeve can be expanded beyond its burst limit, in other words until the hollow profile bursts. Following the bursting of the hollow profile, further expansion of the sleeve takes its place in this area, and there, following completion of the expansion process, assumes the shape of the desired contour of the part. Because its material is more ductile, the sleeve can expand many times more under the influence of high internal pressure than can the hollow profile, without failing as a result of crack formation. Thus a part based on light metal can be manufactured safely with this process that requires very high deformation because of its deformation characteristics. Neither the hollow profile nor the sleeve need to fulfill particular quality requirements so that manufacturing is inexpensive. In addition, there is no significant additional expense for equipment for use in manufacturing. Leaks at the ends of the sleeve also cannot occur in the method according to the invention since, because they abut the tool engraving outside the burst area, they are held in a press fit against the hollow shape by the expansion pressure.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.